1. Field of the Invention
This invention relates to the field of the simultaneous winding and grounding of electroconductive films. More particularly, it relates to photosensitive polyacetylenic systems wherein a film which is electroconductive is wound onto a spool with simultaneous grounding of the film.
2. Description of the Prior Art
Numerous systems are known wherein it is necessary to wind a film upon a spool and wherein the film must be grounded. Normally, such films are electroconductive.
This situation particularly arises in the area of photosensitive polyacetylenic systems. Such systems are disclosed in U.S. Pat. Nos. 4,066,676; 4,581,315; 3,501,310; 3,501,297; 3,501,303; 3,501,308; 3,772,028; 3,884,791; and 3,954,816.
Generally, a film composed of a variety of layers including a crystalline polyacetylene layer fed from a feed spool or reel, is exposed to a source of radiant energy. The radiant energy is directed against the film in a predetermined pattern resulting in an immediate image due to crystalline changes in the polyacetylenic compound. The film is then wound on a wind-up spool. After the desired pattern has been produced on a given length of film, this segment is cut from the film supply reel, and the freshly cut leading edge of the film on the supply spool is threaded through the exposure device and secured onto a take-up spool or reel.
Such films are composed of laminates of a variety of layers, one of which is a conductive layer. Usually, the conductive layer has a thickness in the range from about 1 angstrom to about 0.25 micrometers. The conductive layer limits the capacitance of the charge accepting layer which is normally the image-receptive polyacetylenic crystals which are dispersed in a binder in the film. It serves to dissipate excess and static charges which build up and which otherwise would produce significant defects in the resolution and clarity of the imaged pattern.
More specifically, the radiant energy, in the form of electrons possesses coulombic properties and are subject to deflection by an electrical field. It is thus possible for a considerable electric field to build up as a result of charge deposition on a non-conductive or non-grounded recording medium or film This build-up is sufficient to affect even the trajectory of 15-20 keV electrons. During exposure of a polyacetylenic imaging system using an electron beam recorder, focus problems in addition to image distortions up to 300 .mu.m were observed. These phenomena were ascribed to a charge build-up in the media. Grounding of the conductive layer in the media in the polyacetylenic imaging system was shown to solve these problems.
In order to accomplish this, the conductive layer must be connected to a ground during the exposure process. Since the film is traversing past the exposure device during this treatment, the electrical contact with the conductive layer and the ground must be maintained during movement of the film. Typically, the conductive material is an electrically conductive metal, metal oxide, metal alloy, metal halide, or carbon black. The conductive layer is normally an interior layer of the laminate, i.e., is not on the surface of the film.
Numerous attempts have been made to ground the film by contacting the conductive interlayer with a ground. However, it has proven difficult to simultaneously and continuously expose and wind-up the exposed film and layer.
Presently, grounding is achieved by using a complicated and rather expensive split metallic wind-up spool. In this spool, the leading edge of the film from the supply spool is locked between a set of sharp pins which penetrate through the film and then make contact with the conductive layer. Each time a piece of exposed film is cut from the end, the split spool must be opened and new conductive contact reestablished with the leading edge of the film from the supply spool. This increases the amount of handling and produces a costly interruption in the process. Thus, every time a piece of film is cut, increased cost is added to the process. Also, the contact obtained by this means is unreliable and, of course, the entire procedure is time-consuming.